Deep water offshore drilling platform



Jan. 23, 1968 w. A. SANDBERG DEEP WATER OFFSHORE DRILLING PLATFORM Filed00* 1, '1965 4 Sheets-Sheet l INVENTOR. W/ZZ /,4/1// ,4. 5A/V05606 BY%Z% Jan. 23, 1968 w. A. SANDBERG 3,364,684

DEEP WATER OFFSHORE DRILLING PLATFORM Filed Oct. 1, 1965 4 Sheets-SheetB INVENTOR. W/AZ/d/M ,4. 54/1/95596 Arm/Mari Jan. 23, 1968 w. A.SANDBERG DEEP WATER OFFSHORE DRILLING PLATFORM 4 Sheets-Sheet Filed Oct.1, 1965 INVENTOR. M/L L MM ,4 94/1/05596 Jan. 23, 1968 w. A. SANDBERG3,364,684

DEEP WATER OFFSHORE DRILLING PLATFORM Filed Oct. 1, 1965 4 Sheets-$heet4 INVENTOR. W/AA MM A Sl m/062796 United States Patent 3,364.634 BEEPWATER OFFSHORE DRHLTNG PLATFURM William San herg, 325 S. Orange GroveBlvd, Pasadena, Caiif. 91195 Filed get. 1, 1965, Ser. No. 492,154 aCiaims. or. 61-46) ABSTRACT 9F THE DTSCLGSURE This invention relates todrilling platforms for offshore drilling operations and, moreparticularly, is concerned with a drilling platform which can beassembled and disassembled at the drilling site.

There is a need in offshore drilling exploration for a drilling platformwhich can be transported in pieces and assembled at the location. Onesuch offshore drilling platform is described in Patent 2,772,539 issuedto the same inventor as the present invention.

The present invention is directed to a similar drilling platform but ofimproved design which permits its use in water of substantially greaterdepth and where the bottom terrain is more sloping. Moreover, thepresent improved design of drilling platforms permits twenty or morewells to be drilled from a single platform in contrast to the singlewell which could be drilled from the platform described in theabove-identified patent.

In brief, the present invention relates to a drilling platform of thetype in which a vertical caisson is supported at its lower end at thecenter of a tripod structure resting on the ocean floor. The caisson canbe tilted in relation to the base of the tripod about its lower end topermit the caisson to be truly vertical regardless of sloping orunevenness in the ocean floor at the drilling site. The caisson isrestrained against tilting or shifting under the forces of surface waveaction or seismic disturbances by tension members attached to the outerextremities of the base structure and the upper end of the caisson.

The improved features of the present invention are achieved by a uniquedesign of the engaging structure where the caisson and base of thetripod join. The base of the tripod structure is provided with anannular cylindrical hub having a large central opening only slightlysmaller in diameter than the caisson. Three horizontal arms projectradially outwardly from the hub and are supported at their ends from theocean floor by vertical legs. A supporting annular plate having abeveled inner edge forming a conical surface is mounted on the top ofthe hub. The lower end of the caisson is convexly curved so as to reston the conical surface of the supporting plate. The upper end of thecaisson is secured by tension members or guys extending from the top endof the caisson to each of the vertical supporting legs of the base. Thecaisson can be tilted substantially with relation to the hub while stillretaining mating contact between the supporting plate and bottom of thecaisson. At the same time, the bottom of the caisson remains axiallywithin the center of the opening in the hub. The hub is structurallydesigned to transmit forces through the arms of the tripod base to thelegs resting on the ocean floor. At the same time, the opening in thehub is large enough to permit a large number of conductor tubes toextend out the bottom of the caisson into the ocean floor for slantdrilling a corresponding number of wells from the single platformstructure. The vertical component of force of the caisson is taken bythe conductor tubes directly to the ocean floor. The vertical componentof force of the guys is taken by the weighted vertical legs.

For a more complete understanding of the invention, reference should bemade to the accompanying drawings wherein:

FIGURE 1 is an elevational view of the drilling platform;

FIGURE 2 is a section taken on the line 22 of FIG- URE 1;

FIGURE 3 is an enlarged sectional view taken on the line 3-3 of FIGURE1;

FIGURE 4 is a partial sectional view taken on the line 4-4 of FIGURE 3;

FIGURE 5 is an enlarged sectional detail taken on the line 5-5 of FIGURE3; and

FIGURE 6 is an elevational view showing an intermediate step in theassembly of the drilling platform.

Referring to FIGURE 1, the numeral 10 indicates generally a verticalcaisson which is supported by a tripod structure, including a baseindicated generally at 12 resting on the ocean floor. The upper end ofthe caisson 10 projects above the surface of the water and supports aworking platform structure indicated generally at 14, on which suitabledrilling rigs (not shown) may be supported for drilling into the oceanfloor.

The tripod base structure 12 is provided with three horizontallyprojecting arms 16 which are joined together at their inner ends by anannular hub indicated generally at 18. The arms are removably joined tothe hub by pins 21 which pass through mating flange members 20 and 22secured respectively to the outside of the hub 18 and to the inner endof the arms 16. This arrangement permits assembly of the tripod basestructure at the location before it is permitted to sink to the oceanfloor.

Each of the arms 15 terminates at its outer end in a leg or stanchion24, the lower end of which is designed to impress itself into thematerial of the ocean floor and support the entire tripod structure inbridgelike fashion above the surface of the ocean floor. The legs areweighted by rock or concrete to anchor them in position.

The vertical caisson 143 is constructed with an outer cylindrical wall34 and a concentric inner cylindrical wall 32 with the space between thetwo concentric walls filled with contrete. This provides a rigid shellwhich is capable of withstanding the large pressures that exist at the690 ft. depths at which the lower end of the caisson may be exposed. Thebottom 34 of the casson forms a spherical surface of radius somewhatlarger than the radius of the cylindrical caisson outer wall 36.

The caisson is provided with a plurality of guide pipes 36 which may bearranged in two concentric circles as shown in FIGURE 3. Twenty-foursuch guide pipes are shown by way of example of a typical installation.The guide pipes are joined to and form openings in the bottom wall 34 ofthe caisson and extend upwardly to the top of the caisson to formopenings at the platform 14. The lower ends of the guide pipes areencased in concrete which acts as a weight at the lower end of thecaisson and provides strength to the caisson structure. Watertightbulkheads are located within the inner wall 32 of the caisson at spacedpoints, as indicated at 38. The watertight bulkheads form compartmentswhich can be individually flooded with sea water at the time the caissonis caused to sink into position. The bulkheads also provide lateralsupport for the guide pipes 36.

The lower end of the caisson 1t engages an annular seat 40 mounted ontop of the hub 13. The hub 18 is a hollow annular structure including aninner wall 42 and a concentric outer wall 44 and enclosing end walls 46and 48. The hollow annular interior of the hub 13 is also arranged to beflooded with sea Water for submerging the hub and tripod base structureat the desired location. The hub is provided with suitable valves 49 bywhich sea water can be admitted and compressed air can be pumped in tocontrol the volume of air in the hub at any depth.

The seat 49 has an opening of the same diameter as the inner cylindricalwall 42 of the hub, which diameter is slightly smaller than the outerdiameter of the caisson 14 but larger in diameter than the innerconcentric wall 32 of the caisson it The upper edge of the opening inthe seat 40 is beveled to provide a conical surface which engages thespherical bottom surface 34 of the caisson it). The seat 43 is providedwith at least three vertically projecting guide members 50 havingslanted inner edges 52 which deflect the caisson towards axial alignmentwith the center of the hub 18 as the caisson is lowered into position.

FIGURE 6 shows the manner in which the caisson 10 is brought intoposition at the desired location. The tripod base structure is firstassembled at the surface, flooded and allowed to settle to the oceanfloor. Before the tripod structure 12 is allowed to sink, cables areattached to cable brackets 60 secured to the inner wall of the hub 18.These cables are threaded through a pair of the guide pipes 36 extendingthrough the caisson 10 and brought out to barges or ships. The caisson10 is initially horizontal and floating on the surface of the ocean. Asit is fiooded starting with the lowermost water compartment, the lowerend of the caisson sinks until the caisson assumes a vertical position.The guide cables are then drawn taut by backing off the barges. As theflooding of the caisson continues, it is guided by the cables intoseating position on the seat at Once the caisson 10 is seated in avertical position, conductor tubes 43 are inserted in the guide pipes3-6 and used as piles which are driven into the ocean floor through thebottom 34 of the caisson 1t! and through the central opening in the hub18. Once the conductor tubes are anchored in the ocean floor, theconductor tubes are cemented into position within the guide pipes 36 sothat the vertical load imposed on the caisson by the platform 14 andsuperstructure mounted on the platform is transmitted to the ocean floorthrough the conductor tubes. At the same time, the conductor tubesprovide passages for the drill stern and the subsequent process ofdrilling wells into the ocean floor from the platform 14.

Three guys 62', made up of a plurality of hollow buoyant sections whichare pivotally connected together at their ends, join the legs 24 of thetripod base structure .12 to the platform 14 at the top or" the caisson10. The guys are pre-stressed so that the maximum lateral forces on thecaisson do not overcome the pro-stressed tension.

The above-described structure in spite of the tremendous size and heightof the caisson 10, typically the caisson being 600 ft. high and 40 ft.in diameter, is capable of withstanding large lateral forces imposed bysurface wave action or seismic disturbances which are transmitted to thecaisson It by the surrounding ocean. At the same time, the vertical loadof the caisson and superstructure is transmitted to the ocean floorthrough the pilings. The unique arrangement by which the caisson isguided and seated on the hub permits the tripod base structure to becanted with the ocean floor at a substantial angle to the horizontal. Atthe same time, the hub arrangement provides a sufliciently large openingthat a large number of drill stem conductor tubes may be providedthrough the single caisson structure. This permits twenty or more wellsto be drilled from a single platform by slant drilling techniques.

What is claimed is:

1. A rig for drilling a number of holes in the ocean floor from a singleplatform comprising a base including a hub and radial arms anchored attheir outer ends to the ocean floor and rigidly secured to the hub attheir inner ends, the hub having upper and lower end walls joined byinner and outer concentric cylindrical side walls, the radial arms beingsecured to the hub adjacent the upper and lower end walls, wherebytension and compression forces in the radial arms are transmittedbetween the arms through the annular end Walls, a vertical column havinga cylindrical outer wall and a spherical bottom, an annular seatingmember mounted on top of the upper end wall of the hub having an openingonly slightly smaller in radius than the cylindrical wall of the column,the seating member having a Conically recessed surface adapted to engagethe spherical bottom of the column to permit substantial angular tiltingof the column in relation to the hub, the annular end walls andcylindrical inner wall forming a single opening through the hub belowthe seating member, the column including a plurality of pipes throughwhich conductor tubes extend through the column and the central openingin the hub into the ocean floor for supporting the column, and tensionmembers extending from the upper end of the column to the outer ends ofthe radial arms for transmitting horizontal loads on the column to thebase.

2. Apparatus as defined in claim 1 further including brackets in theopening in the hub and a cable secured to each bracket and extendinthrough a pipe in the column to the upper end of the column at the oceansurface.

References Cited UNITED STATES PATENTS 2,772,539 12/1956 Sandberg6l--46.5 2,901,890 9/1959 Hutchinson 6146 3,036,438 5/1962 Sims 6l46.5 X3,128,604 4/1964 Sandberg 6l-46.5 3,209,544 10/1965 Borrrnann 6146.5

JACOB SHAPIRO, Primary Examiner.

